Cumene is an important intermediate in the chemical and polymer industries, with global cumene production currently exceeding twelve million metric tons annually. Cumene is generally produced by the alkylation of benzene with a C3 feed stream (e.g., a C3 alkylating agent) in the presence of an acid catalyst. Early cumene plants used solid phosphoric acid as the catalyst, but more recently most cumene manufacturers have replaced the phosphoric acid with molecular sieve catalysts. Examples of benzene alkylation processes employing molecular sieve catalysts can be found in, for example, U.S. Pat. Nos. 4,185,040; 4,992,606; and 5,073,653.
Most cumene plants operating today employ propylene as the C3 alkylating agent. However, the increasing cost and scarcity of propylene provides a significant incentive to find alternative C3 alkylating agents. In view of a continuing over-supply of acetone, there has for some time been interest in developing a process for using the excess acetone as a feedstock for producing cumene. For example, European Patent No. 1069099 B1 discloses a process for producing cumene by alkylation of benzene with isopropanol, either alone or in admixture with propylene, in the presence of zeolite beta and under temperature and pressure conditions such that the reaction mixture is completely in the gas phase. The isopropanol is produced by hydrogenation of the acetone coproduced when the cumene is converted to phenol.
Commercial processes for the production of cumene using molecular sieve catalysts can be conducted in either the vapor phase or the liquid phase. However, in view of the improved selectivity and decreased capital and operating costs associated with liquid phase operation, most commercial cumene processes now operate under at least partial liquid phase conditions. Unfortunately, one disadvantage of operating under liquid phase conditions is that the molecular sieve catalysts tend to be more sensitive to the presence of impurities in the feedstocks, particularly polar compounds such as nitrogen compounds. Such impurities reduce the acid activity of the catalyst and hence decrease the cycle time between required regenerations of the catalyst. Although important with conventional processes employing propylene as the only C3 alkylating agent, impurities are particularly challenging with processes using oxygenated propyl compounds, such as acetone and isopropanol, as the C3 alkylating agent, or part of the C3 alkylating agent. This is partly because of the molecular polarity of the acetone and isopropanol, which competes with the adsorption of the polar nitrogen compounds, and partly because acetone and isopropanol are reactive even at room temperature for the formation of higher molecular weight oxygenates.
Thus, development of a viable process for the removal of contaminants from a C3 feed stream containing oxygenated propyl compounds (either alone or admixed with propylene) is contingent upon finding an adsorbent material and conditions that allow selective contaminant reduction without excessive conversion of the oxygenated propyl compounds (and/or propylene) to unwanted by-products. The present invention seeks to provide such a process.